eolivelli commented on a change in pull request #1106: ZOOKEEPER-1416 -
Persistent, recursive watchers
URL: https://github.com/apache/zookeeper/pull/1106#discussion_r331068300
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File path: zookeeper-server/src/main/java/org/apache/zookeeper/ZooKeeper.java
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@@ -3028,6 +3112,77 @@ public void removeAllWatches(String path, WatcherType
watcherType, boolean local
removeWatches(ZooDefs.OpCode.removeWatches, path, null, watcherType,
local, cb, ctx);
}
+ /**
+ * <p>
+ * Set a watcher on the given path that: a) does not get removed when
triggered (i.e. it stays active
+ * until it is removed); b) optionally applies not only to the registered
path but all child paths recursively. This watcher
+ * is triggered for both data and child events. To remove the watcher, use
+ * <tt>removeWatches()</tt> with <tt>WatcherType.Any</tt>
+ * </p>
+ *
+ * <p>
+ * If <tt>recursive</tt> is <tt>false</tt>, the watcher behaves as if you
placed an exists() watch and
+ * a getData() watch on the ZNode at the given path.
+ * </p>
+ *
+ * <p>
+ * If <tt>recursive</tt> is <tt>true</tt>, the watcher behaves as if you
placed an exists() watch and
+ * a getData() watch on the ZNode at the given path <strong>and</strong>
any ZNodes that are children
+ * of the given path including children added later.
+ * </p>
+ *
+ * <p>
+ * NOTE: when there are active recursive watches there is a small
performance decrease as all segments
+ * of ZNode paths must be checked for watch triggering.
+ * </p>
+ *
+ * @param basePath the top path that the watcher applies to
+ * @param watcher the watcher
+ * @param recursive if true applies not only to the registered path but
all child paths recursively including
+ * any child nodes added in the future
+ * @throws InterruptedException If the server transaction is interrupted.
+ * @throws KeeperException If the server signals an error with a non-zero
+ * error code.
+ */
+ public void addPersistentWatch(String basePath, Watcher watcher, boolean
recursive)
Review comment:
yes
You already did a great work and the client with your changes is still
compatibile at 100% with 3.5 servers in case of not using persistent watches.
If we change the protocol regarding watches (adding some watchtype to the
wireprotocol) you will really need a "compatibility flag" on the client
configuration or some more complicated handshake with version/feature discovery.
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